Infiltration and redistribution of perchloroethylene in partially saturated, stratified porous media

Hofstee, C.; Oostrom, Mart; Dane, J. H.; Walker, Roland

doi:10.1016/s0169-7722(98)00101-6

Cited by 48 publications

(41 citation statements)

References 32 publications

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“…The fully implicit integrated finite difference code has been used to simulate a variety of multifluid systems (e.g., Hofstee et al 1998;Oostrom et al 1997Oostrom et al , 1999Lenhard 1998, 2003;Schroth et al 1998;White et al 2004). The applicable governing equations are the component mass-conservation equations for water, organic compounds, and air, expressed in Equations (2.1a through 2.1i):…”

Section: Numerical Modelmentioning

confidence: 99%

Modeling of Carbon Tetrachloride Flow and Transport in the Subsurface of the 200 West Disposal Sites: Large-Scale Model Configuration and Prediction of Future Carbon Tetrachloride Distribution Beneath the 216-Z-9 Disposal Site

Oostrom¹,

Thorne²,

Zhang³

et al. 2008

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Three-dimensional simulations considered migration of dense, nonaqueous phase liquid (DNAPL) consisting of CT and co-disposed organics in the subsurface beneath the two disposal sites as a function of the properties and distribution of subsurface sediments and of the properties and disposal history of the waste. Simulations of CT migration were conducted using the Water-Oil-Air mode of Subsurface Transport Over Multiple Phases (STOMP) simulator.A large-scale model was configured to model CT and wastewater discharge from the major CT and waste-water disposal sites. A base-case simulation was conducted using hydraulic property values used in the base simulations reported in Oostrom et al. (2004;2006a;2006b) for local-scale simulations of the individual CT waste sites. Wastewater disposal resulted in increased water saturations in the Cold Creek Unit and a water table increase throughout the computational domain. The increased water saturations in the Cold Creek Unit reduced the downward movement of DNAPL CT and gaseous CT. Two sensitivity simulations were also performed using reduced permeability values and increased nonwetting-fluid entry pressure values for the Cold Creek Unit. The simulations conducted with smaller Cold Creek Unit permeability values than for the base case resulted in reduced DNAPL CT movement across the water table. For each case, additional simulations were conducted from 1993 to 2007 considering soil vapor extraction (SVE) from the well system in the vicinity of the three CT disposal sites. Partly due to the assumption of equilibrium partitioning between the various phase, considerably more CT was removed in the simulations compared to field observations. In addition to the large-scale simulations, a series of seven local-scale multifluid flow and transport simulations have been completed to quantify DNAPL, aqueous, and gas CT transport in the subsurface of the 216-Z-9 disposal site. This site was chosen for these simulations because, of the three major DNAPL disposal sites, it received the most DNAPL and it has the smallest footprint. For those reasons, previous simulations have shown that DNAPL disposed at this site would be able to penetrate deep into the subsurface 2006a), potentially to below the water table. In addition, CT concentrations of approximately 350,000 µg/kg were reported in a 1-ft thick lens, located at 19.8 m (65 ft) below the ground surface DOE-RL (2006). Six of the seven simulations (imposed cases 1-6) were conducted with imposed CT quantities in the Cold Creek Unit and/or the 1-ft thick silt lens, located in the Hanford 2 unit below the disposal site. The simulation period for these six cases was from 2007 -2107. The seventh case (modeled case) simulated flow and transport following aqueous phase and DNAPL disposal at the site using inventory data and SVE of 53,000 kg after 1993. The simulation period for this case was from 1955 -2107. ivThe computed aqueous CT mass flow rate across the water table for the modeled case is considerably larger than for imposed cases. The ...

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Section: Numerical Modelmentioning

confidence: 99%

Modeling of Carbon Tetrachloride Flow and Transport in the Subsurface of the 200 West Disposal Sites: Large-Scale Model Configuration and Prediction of Future Carbon Tetrachloride Distribution Beneath the 216-Z-9 Disposal Site

Oostrom¹,

Thorne²,

Zhang³

et al. 2008

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“…The fully implicit integrated finite difference code has been used to simulate a variety of multi-fluid systems (e.g., Hofstee et al 1998, Oostrom et al 1997, 1999Oostrom and Lenhard 1998;Schroth et al 1998;White et al 2004). In this section, a brief overview is presented of the governing equations and solution methods.…”

Section: Stomp Simulator and Constitutive Relationsmentioning

confidence: 99%

Carbon Tetrachloride Flow and Transport in the Subsurface of the 216-Z-18 Crib and 216-Z-1A Tile Field at the Hanford Site: Multifluid Flow Simulations and Conceptual Model Update

Oostrom¹,

Rockhold²,

Thorne³

et al. 2006

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Three-dimensional modeling was conducted with layered models to further develop the conceptual model of CT distribution in the vertical and lateral direction beneath the 216-Z-1A tile field and 216-Z-18 cribs and to investigate the effects of soil vapor extraction (SVE). Base case and sensitivity analysis simulations considered migration of dense, nonaqueous phase liquid (DNAPL) consisting of CT and co-disposed organics in the subsurface beneath the two disposal sites as a function of the properties and distribution of subsurface sediments and of the properties and disposal history of the waste. Simulations of CT migration were conducted using the Subsurface Transport Over Multiple Phases (STOMP) simulator.Simulation results support a conceptual model for CT distribution where CT in the DNAPL phase is expected to have migrated primarily in a vertical direction below the disposal trench. None of the simulations predicted that CT in the DNAPL phase would move across the water table below the 216-Z-18 site. Movement of CT in the DNAPL phase across the water table below the 216-Z-1A site was only predicted in simulations with smaller disposal areas and larger volumes, compared to the base case simulation, and in isotropic porous media. Because uncertainties in disposal area and volume exist, movement of CT in the DNAPL phase across the water table in the subsurface below the 216-Z-1A site should be considered as a possibility. However, even if DNAPL moved across the water table in the past, there may not currently be a DNAPL phase in the groundwater beneath the 216-Z-1A site because of dissolution. Results also show that the Hanford 1a geologic unit, located just beneath the 216-Z-1A and 216-Z18 disposal areas, retains more CT DNAPL within the vadose zone during infiltration and redistribution than other hydrologic units. During simulated SVE operations, CT in this unit remained in the subsurface while DNAPL in other layers was effectively removed. Additional characterization of the Hanford 1a unit below the two disposal sites would provide valuable information about the quantity of DNAPL phase CT remaining in the vadose zone. A significant amount of the disposed CT DNAPL may have partitioned to the vapor phase and subsequently into water and sorbed phases. As for the 216-Z-9 site, it is predicted that any continued migration of CT from the vadose zone to the groundwater is likely to occur through interaction of vapor phase CT with the groundwater and not through continued DNAPL migration. The results indicated that SVE appears to be an effective technology for vadose zone remediation, but additional effort is needed to improve simulation of the SVE process through an enhanced understanding of rate-limited volatilization. A total of 34 three-dimensional simulations have been conducted based on a layered EarthVision™ geologic model, which is an interpretation of available geologic data. These simulations consist of one base case simulation and 33 sensitivity analysis simulations. These simulations examined the infilt...

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“…It is well known that structures of different scales, such as sand lenses within a main soil matrix of a different texture, can significantly influence multi-phase flow and transport Hofstee et al 1998;Taylor et al 2001;Rathfelder et al 2001, Oostrom et al 2003Taylor et al 2004;Braun et al 2005). Accordingly, in the second case study three additional simulations were run in order to illustrate the non-passive transport behavior of aqueous methanol mixtures in a heterogeneous soil.…”

Section: Test Case 2: Heterogeneous Soilmentioning

confidence: 99%

“…On the other hand, non-passive transport of some substances through heterogeneous soils may show the coupling of mechanisms or processes that would not occur in homogeneous media. Several studies show the effect of porous medium heterogeneities on 2D flow and transport in the vadose zone (Pan and Wieranga 1997;Walker et al 1998;Wang and Feyen 1998;Hofstee et al 1998;Wildenschild and Jensen 1999a,b;Oostrom et al 2003;Weisbrod et al 2003;Taylor et al 2004;Robert et al 2006). Several of these studies deal with NAPL transport, including the effects of surfactant addition, in soils consisting of a main matrix that contains one or more lenses of different textural types Schroth et al 1998;Walker et al 1998;Rathfelder et al 2001;Taylor et al 2001;Ramsburg and Pennel 2002;Oostrom et al 2003;Ramsburg et al 2004;Taylor et al 2004).…”

Section: Introductionmentioning

confidence: 99%

Non-passive Transport of Volatile Organic Compounds Infiltrated from a Surface Disk Source

Silva

Grifoll

2008

Transp Porous Med

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An unsaturated flow and non-passive transport model for water-soluble organic compounds has been implemented in cylindrical coordinates, with a top boundary condition that accounts for different zones of the surface that can be under infiltration or volatilization independently. We simulated two-dimensional infiltration of aqueous mixtures of methanol from a disk source, its redistribution and volatilization in both homogeneous and heterogeneous soils. Simulations showed that the incoming composition significantly affects volumetric liquid content and concentration profiles, as well as the fraction of infiltrated mass of methanol that is released to the atmosphere. Concentration-dependent viscosity had the major impact on the liquid flow. The differences in volumetric liquid content and normalized concentration of methanol became more pronounced during transport through a soil composed of a clay lens embedded within a main matrix of sandy clay loam texture. Dispersion in the liquid-phase was the predominant transport mechanism when dispersivity at saturation was set to 7.8 cm. However, for dispersivity of 1.0 cm, changes in composition led to changes in surface tension inducing significantly higher liquid flow. In this case, liquid-phase advection was the most active transport mechanism for homogeneous soils and highly concentrated infiltrating mixtures.

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Infiltration and redistribution of perchloroethylene in partially saturated, stratified porous media

Cited by 48 publications

References 32 publications

Modeling of Carbon Tetrachloride Flow and Transport in the Subsurface of the 200 West Disposal Sites: Large-Scale Model Configuration and Prediction of Future Carbon Tetrachloride Distribution Beneath the 216-Z-9 Disposal Site

Modeling of Carbon Tetrachloride Flow and Transport in the Subsurface of the 200 West Disposal Sites: Large-Scale Model Configuration and Prediction of Future Carbon Tetrachloride Distribution Beneath the 216-Z-9 Disposal Site

Carbon Tetrachloride Flow and Transport in the Subsurface of the 216-Z-18 Crib and 216-Z-1A Tile Field at the Hanford Site: Multifluid Flow Simulations and Conceptual Model Update

Non-passive Transport of Volatile Organic Compounds Infiltrated from a Surface Disk Source

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